High and low frequency transmission circuits



v Jam-l3, 1931. D. G. GRIMLEY HIGH AND LOW FREQUENCY TRANSMISSION CIRCUITS Filed Sept. 15, 1925 by A/fy.

1 entr e ll for "range offrequen'cies; r i a 'W'th the ordinary ,arrangement of transv and is overcome by l iatented Jan. 113,- 1931 nonALn;e.'.GRx1u EY,. on mnenwoon, 'NEWJERSEY, AssIGNoR ro liannncrntnrnonn lLABORATORIES, IINCORPQRATED, or NEW-"YORK, N. Y, -coRPoRArIoN or ew YORK 7 7 HIGH AND LOW FREQUENCY mnnnsmssroncinoufls I Application fiIedSeptemher 15Q192e. se ia in; 135,563. a;

' This invention relates to electrical trans mission circuits andlparticularly to circuits frequencies.

' 'An object of the invention is to control p the transmission characteristicscof amplifier circuit a 1 Anoth'er object'of'the invent on is to ob'-.

tain uniform amplification "over a large range of frequencies.

In a preferred embodiment thisinvention 'c'or'np'risesga twostage celectron'klischarge" amplifier with Va feed backi connection from the primary of the interstage transformer to the primary of the input transformer of the first stage. By properly proportioning" the inductance of the interstage'transformeri with respect to its-distributed "capacity and the input capacity of" the second stage, it is p'oss-ible'to obtain a feed-back which will reinforcethe amplification of the WiLYeS in abotl heflloweriand upper portlons of the frequency range so as to obtain substan tially uniform an pllficatlo'n over a wlde formers inarnplifien circuit-spit isfdifiicult to obtain un form amplification were w de r nge offrequencies' due to the effect of the impedance of the transformers and to the shunting effect of the electrode capacityfo'f j thefamplifier tubes,v This loss inamplifica-V -v tion is'particularly noticeable in the upper and lower portions of the frequency range of" the circuit 7 v of this" invention, above described. Y

quency of the range of' frequencies to be ampllfieda This arrangement glues "the fil'ansfoimer Lir emp r ivel i high vqnag "amplifying' w'aves ofialarge range of the regenerative action an output-transformer; 5.

a-nlplicfice i oirat the esonant frequency hichiis desirable for the efdcient operation of the secondstage and produces a' feed backflat. frequencies iboth aborie f and below the resonant fr'equ'ency, which increases the amplification or the first stagejtoj counterc act the lower ehiciency of fthe transformer for frequencies-in those ranges;

- While this inv nt; 11 1s described 111 0011;

nection with a particular circuit'arrangerne'nt it should be understood that" the general principles may; be'applied tovari'dus 'modified circ'uits ithout departing from the spirit of the invention. I the tnnedcircui't may be 'obtfainedby the use other than a second [amplifier stage and the voltagereversal HGCBSSELTY for obtaining n aiding feediback may 7 he oh-i For *example;

of circuits tained by the use of a tertiary Winding or byniaking the connection- 300 the secondaries (if tl'iei transformers, instead of to tl1e"prilnaries. Various; other Inodificzit-ionsv will be circuit illustrating the general principles of this 'lnventlon and Fig. 2 shows a two-stage Referring first to 'readilyysuggestcd:to those skilled in the art; r This invention canbejmorefreadilynnder- 1 stood by re fere'nce to the followingdetailed description Q QIIHBCtiOII with the drawing, in which, 'Figil shows a simple amplifier a vacuum tube amplifierl; to which Waves tohe amplified are supplied through an in: put transformer and which has its output terminals connected to the grid biasing nected in'theusualmanner; p i; Gonnectedgbetween f the anode of, the tube 3 and one fter'lnihzil "of the primary windin of input,- transformer 4; is. a tuned circuit ai n y r p rl jpe'l ngi the 'wi ii f V so gp m eix p I ilalnent-heating, and platebatmm are cor the transformer l. The amount of feedback Will be in'part determined by the 1mpedance of the circuit 6.. Thus, there-rill .be no feed-back at the frequency at which the circuit 6 is tuned as the "inpedance of the circuit is practically i unite its resonant frequency, While there will be appreciabe' feed-back at other frequencies. A

In this Way, by c esigning the c rcu t to be resonant at a mid-frequency of a band of frequencies to be amplified, appreciable feed-back may be obtained both above and belowthe resonant frequency. This will tend to increase-amplificatlon o'f'the circuit for waves 1.

neutralize-the natural ineiliciency or. the amplifier in the lower and upper frequpncy ranges so as give a substantial Uii lIOfm transmission over a Wide ra or frequencies, or the amount of fee may be regulated by properly choothe con stants of the circuit so as to give any desired frequency-ampli" ation, characteristic.

In tn circuit of Fig, Qthe tuned circuit for uing the feed-baclsis obtained by the proper choice fofl inductance for the interstage transformer with respect to the input capacity ,ofthe tube of the second stage. The circuit of FlgiQ COlRIT-LZSGS;tWO vacuum tube amplifiers, lOandfll connected in tandem through an vinterstage transformer .12.

. Each tube is suppliedwith the usual cathode primary heating, grid. biasing and plate batteries. lVavesto beani lified are supplied to the 1nput terminals of the firsttube 10 through the input v terminals of the second stage ,tube 1 1 are connected to theprimary of an output transformer l l. or 1 j Feed-back is obtained byincluding a pertionof the primary winding of't'he input transforiner 13 in the connection 15 fronithe of "the interstage transformer to the cathode'of the tube 10; Thisf'feed-back is made regeneratire by properlypoling the windings of the input transformers Since theoutput circuit of the tube 10 is in eflect a tuned circuit consisting of the mutual inductance of the interstage transformer 12 in l parallel with its distributed capacity and the capacity of the input terminals of thesecond stagetube 11' this gives an arrangement similar'tothat Fig. 1. By making this parallelcircuit resonant atthemid frequency p of-the range of frequencies to be amphneu,

it is possible to obtain increased amplifiea tion in both the lower and upper portions of-the range to compensateforthe natural lower eflicien'cyin those portions produced by the actionof the transformers, and thus to give a uniform over-all characteristic;

7 .By making the transformer 13" resonant at the-same frequencythis cOIIlj ing 'efiect is accentuated.

"those ranges of frequencies. This increased amplification will tend to- I circuit transformer 13 and the output.

While the circuits of Figs. 1 and 2 are similar, one essential difference should be noted, namely, in-the c'rcuit of Fig. 2 the output- 0f the amplifier is taken from the circuit which controls the feed-back instead of from a separate circuit.

Obviously the connections are such that if the tube 10 is the second stage of a multistage amplifier the plate current for that tube maybe drawn from the plate battery of the preceding stage.

lVhat is claimeo is: 1. An amplifier comprising a plurality of stages eachhaving'an. output circuit and a "capacitive input circuit, a transformer having one Winding connected in the output of one stage and a second Winding connected in theinput circuit of a succeedingstage effectively in shunt With the input capacity thereof, and means for securing substantially uniform amplificatlon by said amplifier of impressed Waves of a Wide range of frequencies, said means comprising feedback circuit intercoiniecting the out? put circuit and the input circuit of said one stage and including therein one of the trans- V former windings and the capacity effectively in shunt therewith, the inductance of said shunt therewith forming a resonantcircuit tuned toian intermediate frequency of the.

band ofwaves to be amplified by said combination, and'means for 'securingsubstantially uniform amplification by saidfcombination of said waves over a Wide frequency range, said'means including a feed: 1

back circuit inter-connecting the output and input circuitsiof said. first mentioned device and: effectively includ ng therein said reso nant circuit.

' 3. A multistage amplifier comprising an electron discharge device having input and output terminals ineach. stage, an interstage transformer having a primary Winding connected to the output terminals of 'a device in one stage and asecondary Winding connected to the input terminals of a device in a subsequent stage, said transformer being designed to form a timed circuit with the capacity of the input terminals of said second device at amid-frequency,- of a Wide means comprising a circuit for feeding back waves from the output terminals of said one device to the input terminals thereof, and including a circuit tuned to anintermediate requency within said range, said tuned-circ'uit including as an element-thereof the-mutual inductance of said transformer;

In witness whereof, I hereunto subscribe my name this 14th day of September, A. D.

= DONALD GRIMLEY. 

